Incandescible cathode



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United States Patent O INCANDESCIBLE CATHODE Hendrikus `lohannesLemmens, Marinus Jacobus Jansen, Pieter Willem Haayman, and PetrusCornelis van der Linden, Eindhoven, Netherlands, assignors to HartfordNational Bank and Trust Company, Hartford, Conn., as trustee ApplicationJuly 5, 1952, Serial No. 297,306 Claims priority, applicationNetherlands July 17, 1951 4 Claims. (Cl. 313-346) This invention relatesto an incandescible cathode and more particularly to a cathodecontaining a supply of an alkaline earth compound capable of reductionby a refractory metal to free alkaline earth metal.

Cathodes of the aforesaid type have been described in U. S. Patent2,543,728 to H. I. Lemmens et al. In the cathodes described in thepatent, a reservoir of alkalineearth compounds is located within acavity of a body of refractory material which body has a porous wallportion and is tightly'closed so that the pores of the porous wallportion form the largest connecting passageways connecting the reservoirof alkaline earth compounds with the outside of the cathode. Thealkaline earth compounds disclosed in the said patent are the carbonatesof the alkaline earth metals, for example barium and strontium whichdecompose at elevated temperatures to form the oxides of the alkalineearth metals with release of carbon dioxide. The latter must then bepumped off continuously to maintain a high vacuum in the tube.

` It is an object of the present invention to eliminate the need forcontinuous evacuation of the discharge tube during activation of thecathode in an electric discharge tube.

This and further objects of this invention will appear as thespecification progresses.

In accordance with this invention, the cathode comprises a structureforming an internal cavity, the portion of the structure surrounding thecavity consisting of a refractory metal such as tungsten, molybdenum,tantalurn, zirconium or hafnium. Within the cavity a supply of analkaline earth boride, for example, BaBs or SrBs, and mixtures of thosecompounds is disposed. The cavity is sealed by means of a wall of porousrefractory metal, the pores of this wall forming the largest passagewaysconnecting the cavity to the exterior of the cathode.

The porous wall of the cavity preferably consists of a body of tungstenformed by pressing powdered tungsten and sintering the same attemperatures exceeding 1600n C. in order to obtain tungsten body ofrequired porosity. As the borides do not require a high formationtemperature such as carbonates the tungsten may be sintered as low as1400 C. However, therein very line powder should be used.

The borides of the alkaline earth metals should be preferably in acrystalline state.

Since there is no carbon dioxide formed during the life of the cathode,no exhaust of gas is required. The amount of gas released by a cathodeof this type does not exceed the amount of gas liberated by other partsof the tube and consequently, the cathode only requires a few minutesfor the formation of a monomolecular layer of alkaline earth metal onthe exterior surface.

The invention will be described in connection with the accompanyingdrawing in which the sole figure shows one embodiment of a cathodeaccording to the invention.

The cathode shown in the drawing comprises a porous tungsten plate 1formed as described in U. S. Patent 2,543,728 in order to have thecorrect porosity. The plate is 0.5 mm. thick and 3 mms. in diameter. Thetungsten plate 1 together with a cup-shaped molybdenum member 2 with asharp upper edge 3 to which the tungsten plate is secured forms aninternal cavity in which a supply 4 of about 1 to 5 mgs. of bariumboride is disposed. Plate 1 is welded to the edge 3 to tightly seal thecavity. The cathode is heated by means of a heater 5 disposed within atubular extension 6 of the cup-shaped molybdenum member.

While the invention has been disclosed in connection with a specificembodiment thereof other modifications will be readily apparent to thoseskilled in this art with out departing from the spirit and scope of thisinvention as delined in the appended claims.

What we claim is:

1. A dispenser cathode comprising a structure forming an internal cavityand having an electron emissive surface, a porous sintered body ofrefractory metal forming part of the wall of said structure, saidstructure being tightly closed with the pores of said wall portionconstituting the largest passageways connecting the cavity to saidelectron emissive surface, and a supply within said cavity of analkaline earth material capable of furnishing free alkaline earth metalto said electron-emissive surface at a rate sufficient to maintain amonomolecular layer of alkaline earth metal thereon, said materialconsisting essentially of an alkaline earth boride.

2. A dispenser cathode comprising a structure forming an internal cavityand having an electron emissive surface, a porous sintered body oftungsten forming part of the wall of said structure, said structurebeing tightly closed with the pores of said wall portion constitutingthe largest passageways connecting said cavity to said electronemissivesurface, and a supply within said cavity of an alkaline earth materialcapable of furnishing free alkaline earth metal to said surface at arate sutlicient to maintain a monomolecular layer of alkaline earthmetal thereon, said material consisting essentially of an alkaline earthboride.

3. A dispenser cathode as claimed in claim 2 in which the alkaline earthmaterial c-onsists essentially of barium boride.

4. A dispenser cathode as claimed in claim 1 in which the alkaline earthmaterial is a mixture of barium boride and strontium boride.

References Cited inthe file of this patent UNITED STATES PATENTS1,720,654 Wein July 9, 1929 1,936,334 Miesse Nov. 21, 1933 2,121,589Espe June 21, 1938 2,543,728 Lemmens et al Feb. 27, 1951 2,647,216 BrownJuly 28, 1953

1. A DISPENSER CATHODE COMPRISING A STRUCTURE FORMING AN INTERNAL CAVITYAND HAVING AN ELECTRON EMISSIVE SURFACE, A POROUS SINTERED BODY OFREFRACTOR METAL FORMING PART OF THE WALL OF SAID STRUCTURE, SAIDSTRUCTURE BEING TIGHTLY CLOSED WITH THE PORES OF SAID WALL PORTIONCONSTITUTING THE LARGEST PASSAGEWAYS CONNECTING THE CAVITY TO SAIDELECTRON EMISSIVE SURFACE, AND A SUPPLY WITHIN SAID CAVITY OF ANALKALINE EARTH MATERIAL CAPABLE OF FURNISHING FREE ALKALINE EARTH METALTO SAID ELECTRON-EMISSIVE SURFACE AT A RATE SUFFICIENT TO MAINTAIN AMONOMOLECULAR LAYER OF ALKALINE EARTH METAL THEREON, SAID MATERIALCONSISTING ESSENTIALLY OF AN ALKALINE EARTH BORIDE.